This book will teach you how to use Swift to apply functional programming techniques to your iOS or OS X projects. These techniques complement object-oriented programming that most Objective-C developers will already be familiar with, providing you with a valuable new tool in your developer's toolbox. We will start by taking a look at Swift's new language features, such as higher-order functions, generics, optionals, enumerations, and pattern matching. Mastering these new features will enable you to write functional code effectively. After that, we will provide several examples of how to use functional programming patterns to solve real-world problems. These examples include a compositional and type-safe API around Core Image, a library for diagrams built on Core Graphics, and a small spreadsheet application built from scratch.